1. Field of the Invention
The present invention relates to an X-ray source for emitting a characteristic X-ray and a fluorescent X-ray analyzing apparatus using the X-ray source.
2. Description of the Related Art
In an ordinary X-ray source, electrons accelerated at a high voltage enter an anode constituting a target thereby to emit the bremsstrahlung X-ray and the characteristic X-ray unique to the target (see, for example, Jpn. Pat. Appln. KOKAI Publication No. 2004-28845, pp. 4-5, FIGS. 1 and 2).
The bremsstrahlung X-ray is a continuous energy spectrum configured of white and has a spectral distribution changing with the incident electron energy. The characteristic X-ray, on the other hand, not dependent on the electron energy, is monochromatic and has a single energy distribution unique to the target. In fluorescent X-ray analysis, the energy distribution of the signal of the fluorescent X-ray emitted at the time of incidence of the characteristic X-ray into the specimen is measured to identify the type and amount of the elements in the specimen. For this purpose, various X-ray sources devised to improve the analysis performance are used.
In the fluorescent X-ray analyzing apparatus, the specimen is excited using the characteristic X-rays having a known spectrum. In this way, the signal of the fluorescent X-ray and the noise component constituting the scattering of the incident X-ray are easily distinguished from each other, which enables element analysis at a high S/N ratio. In view of this, attempts have been made at practical application of an X-ray source that emits an almost monochromatic X-ray spectrum.
FIG. 29 shows an example of a general configuration of a high resolution fluorescent X-ray analyzing apparatus using the characteristic X-ray described above. In this case, an ordinary X-ray source 1 is used, and a continuous X-ray 2 constituting the primary X-ray of the continuous energy spectrum emitted from the particular X-ray source 1 is applied to a secondary target 3. Thus, a characteristic X-ray 4 is emitted and irradiated on a specimen 6 through a collimator 5 arranged externally, so that a fluorescent X-ray 7 emitted upon excitation of the elements on the surface of the specimen 6 is detected by an X-ray detector 8.
In the emission system of the characteristic X-ray 4 having this configuration, the X-ray source 1 and the secondary target 3 are required to be arranged in spatial relation to each other. The continuous X-ray 2 is emitted in the entire peripheral direction of 4π, the strength of which reduces in inverse proportion to the square of the distance. In the conventional configuration, therefore, the efficiency of irradiating the secondary target 3 with the continuous X-ray 2 emitted from the X-ray source 1 is low. To increase the strength of the characteristic X-ray 4 emitted from the secondary target 3, therefore, the provision of a large-output X-ray source 1 is required. This increases the size of the high-resolution fluorescent X-ray analyzing apparatus, the power consumption and the X-ray shield scale, resulting in an increased cost which restrains the spread of the use thereof (see, for example, “Present Situation and Outlook of Fluorescent X-Ray Analysis” by Izumi Nakai, Applied Physics, Vol. 74, No. 4, 2005, pp. 455-456).
Also, FIG. 30 shows the total reflection X-ray fluorescence analysis (TXRF) now widely used for inspection of the surface contamination of a semiconductor wafer serving as the specimen 6. The characteristic X-ray 4 is required to enter the semiconductor wafer surface at a very small angle of not larger than 0.1° as consistently as possible, and is suitably, therefore, a sheet beam, for example, including a sectorial fan beam.